1. Field of the Invention
This invention pertains to a controller for controlling discharge capacity of a compressor used for executing a cooling cycle of an automobile air conditioner.
2. Description of the Related Art
An extensive variety of discharge-capacity controllers of automobile air conditioner compressors have been manufactured in the past. One well-known type of said controllers is introduced in Japanese Laid-open Patent Publication 62-94748; in this type of controller, a desired cooling temperature of evaporator is determined according to the temperature of the air vented out of the air vent, and the discharge capacity of the compressor is controlled at variable levels to produce the desired cooling temperature.
This type of controller is characterized by the fact that the aforementioned desired cooling temperature changes, according to environmental conditions inside/outside the passenger compartment and set temperature inside the passenger compartment. For example, if the outdoor temperature is low when the air conditioner is turned on, the cooling load is lower than that when the outdoor temperature is high, unless a specific condition is present; the temperature is set high, the cooling load is lower than that when the temperature is set low, as long as other environmental conditions remain unchanged; therefore, the desired cooling temperature can be set high.
However, if the temperature is manually set higher in the passenger compartment when temperature and humidity are high, as, in fact, they are in summer in Japan, the desired cooling temperature rises, which reduces the cooling capacity of evaporator, and the dehumidifying capacity, accordingly, is reduced, often causing the passengers to feel humidity, which is uncomfortable.
On the other hand, when the outdoor temperature is low in rainy weather, the desired cooling temperature rises since the cooling load is lower than that when the outdoor temperature is reduced, causing an insufficient dehumidifying effect and generating fog on the wind shield, which is a problem.
As to the dehumidifying function, Japanese Laid-open Patent Publication H2-290712 introduces one well-known example, in which the dehumidifying capacity of the evaporator is reduced by reducing the compressor's discharging capacity when humidity is lower than a specific level in the passenger compartment, and thus, the air-mixing door is controlled to prevent the changes in the temperature of vented air so that the temperature of the vented air will not rise. In other words, this function prevents the humidity from being reduced in the passenger compartment, by reducing the dehumidifying capacity while keeping the temperature of the vented air at the same level.